(1) Field of the Invention
The present invention relates image forming apparatuses, such as printers, copiers, and the like. In particular, the present invention relates to a technology for improving the productivity of print operation of an image forming apparatus that executes a delay process to provide a wait time by suspending the execution of print operation or by reducing the print speed. The delay process is executed with the aim of preventing the decrease in image quality or deterioration of the apparatus parts due to changes in temperature and the like in the image forming apparatus during print jobs.
2) Description of the Related Art
To improve the print operation productivity, image forming apparatuses, such as printers, copiers, and the like are required to process print operation at a higher processing speed. However, by continually processing print operation at high speed, the temperature of the image forming apparatus tends to increase. This may cause problems such as the thermal deterioration of apparatus parts, the image quality degradation as a result melting and subsequent sticking of the toner in a developer, and the like.
In a two-sided printing mode, recording sheets after the thermal fixing are stacked on one another at high speed in an exit tray. Therefore, heat accumulated in the recording sheets cannot be dissipated easily, which increases the risk of tacking.
For example, JP 10-010916-A discloses one technology for solving the problems noted above. According to the disclosure, a delay process is executed to slow the processing speed by suspending the execution of print operation to provide a wait time when the temperature in the apparatus (in the fixing device) exceeds a predetermined temperature or by lengthening the sheet transfer intervals by a predetermined extent to reduce the print speed when the numbers of prints exceeds a predetermined number. This prevents the temperature rise in the apparatus to solve the problems noted above.
Unfortunately, the delay process described above slows the processing speed of print operation, which decreases the print operation productivity. The decrease in print operation productivity is especially notable when the duration of the delay process is prolonged.
The decrease in print operation productivity caused by a delay process may be suppressed by shortening the sheet transfer intervals after the delay process (see JP 2006-251060-A). Yet, the shorting of sheet transfer intervals may lead to a temperature rise in the apparatus, which may result in another delay process to be executed during the print operation. In such a case, the print operation productivity is decreased even more.